It is known that the usual heated glass panes, especially those which are used for rear windows in automobiles, contain a network of electrically conductive wires or bands incorporated in the glass or applied on its surface. This network emits sufficient heat when it is connected to the terminals of the vehicle battery, in order to thaw the frost covering the abovementioned window and thus restore after a certain time to its normal transparent state. Of course, this defrosting action manifests itself first in the immediate vicinity of the conductive zone. The intermediate zones remain opaque for a certain time after the current is applied. As these conductive zones are generally opaque in themselves especially if they are strips of metallized paint, such a partial defrosting is insufficient for a time, to assure a total visibility through the glass pane; in fact, the glass pane does not have generally sufficient visibility until the defrosted zones are considerably extended on all sides of the conductive strips.
It was sought to remedy this inconvenience by making the conductive zones thinner and closer to each other or by the application on the glass of a conductive uniformly transparent layer, for example, a deposit of a conductive film of tin oxide with a thickness of several .mu.m. Such solutions yield a practically homogeneous heating of the glass pane and its uniform defogging or defrosting. Nevertheless, such a remedy has a serious flaw, which is tied to the fact that the rise in temperature of a glass pane of a uniform thickness with a uniform conductive layer, occurs more slowly than in the favored zones situated in the immediate vicinity of the conductive strips of a classic heated glass pane. As a result, although a glass pane with a homogeneous conductive layer defrosts itself evenly, it does not become sufficiently transparent for effective vision until after it has been energized for a relatively long time.
Taking into account the fact that it is hardly possible in the case of the automobile to increase considerably the consumed electrical power and thus increase the defrosting speed (the accepted power for defrosting a rear car window is on the order of 5 to 250 W), the previously cited drawbacks have been overcome by concentrating the heating on certain transparent portions of the glass panes. These portions, once clarified, create a majority of transparent areas, the total of which assures a useful and sufficient visibility through this partially defrosted glass pane.
Thus, French Pat. No. 2.075.352 describes a heated glass pane comprising three transparent conductive regions, alternating with nonconductive regions (see page 2, lines 22-30 and FIG. 1). Though it is not specifically indicated in this reference that the transparency of the conducting zones alone give a sufficient vision through the glass pane, this seems to be evident enough from the disposition of these zones in FIG. 1 of the drawing.
With regard to the manufacturing of the transparent conductive regions, the above reference mentions the technique of deposition of bismuth oxide, covered with gold by vacuum deposition.
French Pat. No. 1.116.234 describes the deposition by atomization of a layer of SnO.sub.2 on a glass plate, heated in such a manner as to form on it a transparent electricity-conductive film (see p. 1, col 2, lines 20-26). Nozzles spray horizontally an atomized solution against the glass plate, oriented vertically and perpendicularly to the atomized jets, and the panes are moved laterally in the field of the spraying of the jets. The operation is repeated back and forth until the desired thickness is obtained.
Moreover, it is indicated, p. 5, col. 1, lines 16-25, that the ends of the windshield (made out a glass plate) does not contain the deposit.
A third reference, the U.S. Pat. No. 2,833,902, concerns the deposits of layers of SnO.sub.2 on the glass plates through atomization of a solution of an organic compound of tin. This process is illustrated by FIG. 4, where a set of four atomizing nozzles is seen spraying a solution of a tin compound on a heated substratum moved relative to the nozzles. Still it should be noted, that according to the sketch of FIG. 3 of the same patent the two superposed rows of traces left by the spraying from the nozzles, crisscross each other (this is evidently necessary in order to obtain a homogeneous layer on the surface of the entire plate), which can not be at all suitable for the depositing of the conductive strips, as is desired for the present invention.
A fourth reference, the French Pat. No. 1.165.645, concerns the depositing of transparent conductive layers in which the transmission does not exceed 72% (see p. 4, Example 4). These layers are obtained by depositing transparent metallic films on a transparent base. These films can contain gold, silver, copper, iron, nickel or other metals.
The U.S. Pat. No. 3,475,588 concerns defrosting glass panes containing a succession of contiguous heating regions. Each of these zones can be heated according to an independent program. It does not deal, therefore, with a glass which includes an alternation of conductive and nonconductive spaces as in the present invention.
The French Pat. No. 1.531.506 describes conductive glass panes which can contain either opaque resistances or, conductive transparent independent zones which cover the quasi totality of the glass pane surface (see p. 3, col. 2 at the top and FIG. 5). This arrangement is not advantageous, because it is much too similar to the technique in which the entire glass pane is heated, a solution whose drawbacks were described above.
A seventh reference, the U.S. Pat. No. 2,564,677, describes the preparation of conductive iridescent films, of oxides on substrates by the atomization of salt solutions. It does not seem that the last reference contains data applicable to the production of glass panes of the type of the invention, due to the lack of transparency of such iridescent deposits.